The present invention relates generally to a reflector structure in a multi-domain liquid crystal display (MD-LCD), and more specifically to a reflector structure that is used in a reflective or semi-reflective multi-domain liquid crystal display and the method for manufacturing the same.
The market for liquid crystal display (LCD) panels is growing rapidly. Most conventional reflective, or semi-reflective liquid crystal displays are horizontally aligned twisted nematic. Liquid crystal directors of these liquid crystal displays form a single domain in a transmittive region or reflective region when an electrical voltage of a gray scale signal is applied. As shown in FIG. 1a, directors of liquid crystal molecules 103 forming a single domain in the layer between two dielectric substrates 101 and 102 point to the same direction, and have the same pre-tilt angle when a voltage is applied. In a liquid crystal display having multiple domains, directors of liquid crystal molecules 113 shown in FIG. 1b point to different directions, and have different pre-tilt angles.
The gray scale switching effect of liquid crystal molecules in a multi-domain liquid crystal display is better than that of liquid crystal molecules in a single domain liquid crystal display. Also, the gray scale inversion (GSI) region of liquid crystal molecules in a multi-domain liquid crystal display is smaller than that of liquid crystal molecules in a single domain liquid crystal display. These facts can be seen from equal contrast ratio contours shown in FIGS. 2a-2c. 
FIG. 2a shows equal contrast ratio contours of liquid crystal molecules in a single domain liquid crystal display where the applied voltages are 1.5 volts and 2.5 volts and the pre-tilt angle of liquid crystal molecules is 1xc2x0. Label 201 indicates the gray scale inversion region of liquid crystal molecules in the single domain liquid crystal display. FIG. 2b shows equal contrast ratio contours of liquid crystal molecules in a single domain liquid crystal display where the applied voltages are 1.5 volts and 2.5 volts and the pre-tilt angle of liquid crystal molecules is 12xc2x0. Label 203 indicates the gray scale inversion region of liquid crystal molecules in the single domain liquid crystal display. FIG. 2c shows equal contrast ratio contours of liquid crystal molecules in a multi-domain liquid crystal display where the applied voltages are 1.5 volts and 2.5 volts and pre-tilt angles of liquid crystal molecules are between 1xc2x0 and 12xc2x0. Label 205 indicates the gray scale inversion region of liquid crystal molecules in the multi-domain liquid crystal display. From these figures it can be seen that the gray scale inversion region in a multi-domain liquid crystal display is smaller than that in a single domain liquid crystal display. Therefore, a multi-domain liquid crystal display has a better gray scale switching effect and an improved viewing angle.
The present invention has been made to overcome the above-mentioned drawbacks of a conventional reflective, or semi-reflective liquid crystal display in which the arrangement of liquid crystal molecules forms a single domain. The primary object is to provide a reflector structure that can be used in a reflective, or semi-reflective multi-domain liquid crystal display and the method for manufacturing the same.
According to the invention, the reflector structure in a multi-domain liquid crystal display comprises an active matrix device structure having regions of various height levels, a diffusing layer, and a structure of multi-domain reflective layer. The diffusing layer is formed above the active matrix device structure with multiple extruded bumps of various film thickness and various heights and shapes. The multi-domain reflective layer is deposited on the diffusing layer.
According to the invention, after the cell structure of the multi-domain reflective layer is fabricated, liquid crystal cells form multiple domains within a pixel area. Comparing with conventional single domain liquid crystal displays, the multi-domain liquid crystal display of the invention has a better gray scale switching effect and an improved viewing angle. In addition, the reflector structure of the invention forms multiple domains within a pixel area. Therefore, it has advantages of various reflective angles and good reflective effects. The quality of LCD panel is hence improved.
The reflector fabrication process for a liquid crystal display of the invention uses primarily conventional process for a metal or an insulation layer of an active matrix device to form multiple domains within a pixel area. The reflector fabrication process comprises the preparation of a dielectric substrate and the fabrication of an active matrix device, and a structure of a multi-domain reflective layer. During the fabrication, a dielectric substrate having top and bottom surfaces is first prepared. An active matrix device structure is formed on the dielectric substrate by using multiple photo-masks. The active matrix device structure has at least one region of different height level. A structure of the multi-domain reflective layer is then formed on the active matrix device structure with regions of various height levels by using a multi-gap reflector process.
According to the invention, the film thickness of the structure of the multi-domain reflective layer is different at different locations. The diffusing effect is different too. After the cell structure of the multi-domain reflective layer is formed, the average cell gap effect is also different. Therefore, the optical effect of the LCD has an average effect to improve the grayscale. In addition, the diffusing layer formed above the active matrix device structure has multiple extruded bumps of various film thickness and various heights and shapes thereon. Therefore, the diffusing effect is better.
The structure of the multi-domain reflective layer of the invention can be used in a reflective or semi-reflective twisted nematic (TN), super twisted nematic (STN), thin film transistor (TFT), or thin film diode (TFD). After coating a reflective metal layer and forming the cell structure of the multi-domain reflective layer, the multi-domain structure can be used in a reflective or semi-reflective TFT-LCD such as self-compensated twisted nematic (SCTN), reflective twisted nematic (RTN), reflective electrical controlled birefrigence (R-ECB) or mixed mode twisted nematic (MTN) TFT-LCD.
The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.